Method and apparatus for igniting well heaters

ABSTRACT

Ignitors are provided for initiating fuel fed well heaters located adjacent earth formations in a wellbore. The ignitors are battery powered and subsist independently downhole. Batteries are used to provide current to a heating element or, in conjunction with an oscillator and transformer can be used to generate an electric arc using a spark gap. Additionally, a catalytic ignitor can be used in conjunction with a hydrogen containing fuel gas, thereby providing a spontaneous hydrogen and air reaction. The hydrogen-air reaction raises the temperature to that of natural gas ignition.

United States Patent 1151 3,680,635

Berry et a]. [4 1 Aug. 1, 1972 [54] METHOD AND APPARATUS FOR 3,109,482 11/1963 OBrien 166/59 X IGNITING WELL HEATERS 3,113,623 12/1963 Krueger ..166/59 1 I 3,223,165 12/1965 Hujsak ..166/59 X [m :1"; im? mgi gi 3,420,300 1/1969 Todd ..166/59 x Tex 1,124,347 1/1915 Snelling ..23/288 J 1,525,824 2/1925 Palmer ..23/288 .1 [73] Assignee: glib 011! Co p y (Delaware), 1,792,337 2/1931 Wallin ..431/262 X a as, ex. 0, 1969 Primary Examiner-Stephen J. Novosad [22] Filed Dec 3 Attomey-George L. Church, Donald R. Johnson, PP N04 10 Wilmer E. McCorquodale, Jr. and John E. Holder 52] us. c1. ..166/300 166/59, 166/60, TR

- v 166/302, 23/288 J l ABS CT [51] Int. Cl. ..EZlb 43/24 lgmtors are p o ided for initiating fuel fed well heaters [58] Field of Search ..166/57, 59, 63, 60, 299, 300, located adjacent earth formations in a wellbore. The 166/65 R; 431/128, 132, 258, 259, 262, 263, ignitors are battery powered and subsist independently 202; 175/1 1, 14, 4.6, 4.56; 23/288 J; 60/30 downhole. Batteries are used to provide current to a heating element or, in conjunction with an oscillator [56] References Clted and transformer can be used to generate an electric are using a spark gap. Additionally, a catalytic ignitor UNITED STATES PATENTS can be used in conjunction with a hydrogen containing 2,427,377 9/1947 Zschokke 166/65 R x 1 fuel g e y providing a spontaneous hydrogen 2,620,029 12/1952 T h k at l, 166/65 R X and air reaction. The hydrogen-air reaction raises the 2,636,445 4/1953 Tutton ..166/59 X p tu e t th o atural gas ignition. 2,732,016 l/l956 MacLeod ..166/299 X s,032,1 10 5/1962 Hanes et a] ..l66/65 R x 7 Claims 10 Brawl"! B sum 2 OF 2 NATURAL GAS FUEL PUMP F IG 4 m/VE/vmRs DALE w ZADOW ATTORNEY N E G O R D Y H HOLLAND J. BERRY WlLLlAM C. HARDY Ill METHOD AND APPARATUS FOR IGNITING WELL HEATERS BACKGROUND OF THE INVENTION This invention relates to ignitors for well heaters, and is related to two co-pending cases filed of even date herewith and entitled METHOD AND APPARATUS FOR CATALYTIC IGNITION OF EARTH FORMA- TIONS, Ser. No. 889,059, filed Dec. 30, 1969, now abandoned, together with a Continuation-In-Part of Ser. No. 889,059, entitled METHOD AND AP- PARATUS FOR CATALYTTCALLY HEATTNG WELLBORES, Ser. No. 92,836, filed Nov. 25, 1970, and METHOD AND APPARATUS FOR IGNITION AND HEATING F EARTH FORMATIONS," Ser. No. 889,061, 'filed Dec. 30, 1969. Several methods have been utilized to provide heat to well formations for the purposes of in situ combustion and well stimulation. Well stimulation is provided by heat in that the viscosity of the hydrocarbon in the formation is lowered and paraffin adjacent the wellbore is melted.

in situ" combustion involves igniting the hydrocarbon in the formation so'that the heat from the combustion lowers the viscosity of the oil in front of it and gasifies lighter hydrocarbons, thereby providing a pressure to drive the hydrocarbons in the direction of a producing well. The in situ" combustion process involves several steps. First, air is injected into the oil bearing formation through an injection well. The injection pressure should be sufficient tocause the airto flow through the formation from the injection well to one or more producing wells, and it is injected at a sufficient rate to support a vigorous combustion reaction of a fraction of the oil in the formation. Additionally, the air pressure forces the oil away from the casing, so that the well is relatively free of liquids.

In order to initiate a combustion reaction in most oil bearing formations, it is necessary to inject heat along with the air. The heat is carried by the air into the reservoir where it contacts the formation oil. By flowing a sufficient volume of hot air into the reservoir, the cool oil in the vicinity of the injection well is heated to its ignition temperature and commences to burn.

There are several-methods of igniting the oil in the formation including the use of downhole electrical heaters, downhole gas burners, and spontaneous combustion reactions occurring when unheated air is injected into the formation. The downhole electrical heater is used primarily in shallow wells because of the limitations caused by the necessity of usingelectrical cables from the surface to the heater. At depths greater than 3,000 feet, the voltage drop in the cables currently in use results in a considerable reduction in the voltage available to the heater. Moreover, because of the mandatory small cable size, the allowable line current must be limited to prevent damage to the cable insulation by overheating. Voltage dissipation due to the cable resistance would require initial voltages in excess of what can practically be provided and safely operated.

Spontaneous combustion reactions generally occur in naphthenic crudes, and seldom occur in paraffinic crudes. Therefore, gas burners have been employed for most deep paraffinic wells. However, there have been problems related to downhole gas burners in that well damage occurs frequently, due to the intense heat generated by gas combustion and the method for igniting the heater. Ordinarily, in downhole-gas burners an orifice or nozzle is surrounded by a cylindrical heat shield, and is runv on standard oil field tubing to the vicinity. of the top of the formation which is to be heated. Gas is flowed down the tubing through the nozzle and into the heat shield. Air is flowed. down the annular space between tubing and thecasing tothebottom of the wellbore wherepart-of the enters the heat shield and mixes with'the. gas entering the formation being heated. When the burner is ignited, heat from thegas combustion is transferred to the'balance of the which isenteringthe formation. Thisheated air raises the temperature in the-formation surrounding the wellbore untilthe formation hydrocarbons are ignited. Upon ignition of the formation, fuel gas is no longer injected, and vairis'pumped to the formation to support combustion of .the formation hydrocarbons.

To ignite this gas-air mixture, pyrophoric chemicals have generally been used. These chemicals are in wide use and are highly combustible in air at standard conditions. When pyrophoric chemicals are used, special precautions mustbetakemOne such. precaution is a purging of the lubricator and tubing of all air, generally with nitrogen, thus deprivinglthe pyrophoric chemical of air until it reaches the heater. This method of ignition is often not successful, since the fuel mixturemust be present in proper proportions toinitiatecombustion of the fuel gas. If the fuel gas and. air mixture is too rich when contacted by the pyrophoric chemicals, as explosion will probably occur, causing serious damage to the heat shield, tubing, casing, and formation. When the fuel-air mixture is too lean,-the pyrophoric chemicals will notignite the mixture, and the process has to be repeated. The rich and lean mixtures are caused by poor mixing, thereby creating areas which are predominantly fuel-ga or Poor mixing. is notuncommon,

and explosions resulting-therefrom are not infrequent.

.Because of such problems asset forth above, it is an object of the present invention to provide new andimproved well heater ignitors.

SUMMARY OF THEINVENTION provided, it is necessary tochange the direct current to alternating current, and to increase the voltage with. a step-up transformer. The electrical energy then proceeds through a spark gap configuration.

A catalytic ignitor is provided intubular form, having permeable interior and exterior walls, with a baffling material and'catalyticmaterial located between the permeable walls. Fuel gas containing hydrogen is provided to the interior of the ignitor,-and air is provided to the exterior of the ignitor. The hydrogen and air spontaneously react in the presence of the catalyst. This reaction provides sufficient heat for ignition of natural gas and air.

A complete understanding of this invention may be had by reference to the following description, when read in conjunction with the accompanying drawings illustrating embodiments thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 1A depict a battery powered ignitor, including apparatus for generating an electric arc;

FIGS. 2 and 2A illustrate a battery powered ignitor capable of delivering high voltage;

FIGS. 3, 3A, 3B, and 3C illustrate a battery powered ignitor to be used in conjunction with a heating element built into a heater; and I FIGS. 4 and 4A depict a catalytic ignitor.

. DESCRIPTION OF THE PREFERRED EMBODIMENTS trical energy is then increased bya step-up transformer.

Thisequipment is illustrated in FIG. 1A. Located on the electrode probe 74 is a stopping member 88 which isadjustable in that it can belocated along the entire length of the electrode probe 74. The stopping member 88 is used to contact a well heater located in a wellbore such asthose described in greater detail in co-pending application entitled METHOD AND APPARATUS FOR IGNITION AND HEATING OF EARTH FOR+ MATIONS, Ser. No. 889,061 filed of even date herewith. Upon the stopping member 88 contacting the well "heater, the weight of the batteries closes pressure switch 80. Pressure switch 80 consists of springs 90 and I electrical contacts 92 and 94. In FIG. 1A is an illustration of the circuitry between pressure switch 80 and electrode probe 74.. Batteries in battery pack 70 provide direct electrical current to oscillator 78, which converts the direct electrical energy to alternating elec trical energy. The alternating energy is then supplied to high voltage step-up transformer 96, which increases the voltagebeing supplied to electrodes 82. Referring once again to FIG. 1, there is then provided high voltage alternating electrical energy to the spark gap 86.

Thus, in operation, when the ignitor 72 is lowered into the wellbore by wire line 76, the batteries are not connected to the electrode 82. Upon the stopping member 88 contacting a heater located in a wellbore, the pressure switch 80 is closed because of the compression of springs 90 by the weight of batteries 70. When pressure switch 80 is closed, the energy is supplied by battery 70 through the oscillator 78 and high voltage step-up transformer 96, to the electrodes 82. Sufficient voltage should thenbe available to create electric arcs across spark gap 86, thereby initiating combustion of fuel gas being supplied to the heater.

FIG. 2 illustrates a similar ignitor to the one shown in FIGS. 1 and 1A, with the exception that there is no spark gap configuration located at the end of electrode probe 74."This ignitor is used in conjunction with the well heaters having spark gaps built therein shown in co-pending application of even date herewith entitled ME'IHOD AND APPARATUS FOR IGNITION AND HEATING OF EARTH FORMATIONS, Ser. No. 889,061. A pressure switch as shown at 80 in FIG. 1 is not necessary in this ignitor, since there is no connection between the high voltage at electrodes 82 and a spark gap until the ignitor is in contact with the heater. As in FIG. 1, batteries attached to wire line 76 are connected to an electrode probe 74 which terminates with electrodes 82. Between batteries 70 and the electrode probe 74 is located the circuitry necessary for supplying high voltage to the electrodes 82.v Thiscircuitry is illustrated in FIG. 2A. There batteries 70 supply direct electrical energy to oscillators 78 which convert the direct current to alternating current. The current is then supplied to high voltage step-up transformer 96 where the voltage is increased sufficiently to supply the energy necessary for an electric arc. Thus when the ignitor 72 is located in a well heater having a spark gap configuration located therein, the contact of the electrodes 82 with the spark gap in. the heater causes an electric arc across the spaced electrical contacts in the spark gap.

FIG. 3 is illustrative of a battery powered ignitor for use with well heaters that have heating elements located in the heater. The batteries 70 attached to wire line 76 have electrodes 82 attached to it by electrical cable 79. When lowered into a wellbore forigniting a well heater located at the bottom of the wellbore, the electrodes 82 come into contact with mating contact electrodes'52 illustrated in FIG. 3B. These mating electrical contacts 52 are built into the heater, and'are attached to heating element 44, which is essentially a resistor. A catalytic heater with a heating .element 44 contained therein has been shown in FIG. 3C. When in contact, electrical current flows from the electrodes 82 to the heating element 44, thereby generating heat for igniting the well heater.

FIG. 3A illustrates the bottom of the ignitor shown in FIG. 3 illustrating how the electrodes 82 are arranged on'the ignitor. In lieu of having the'heating element 44' constructed in the heater,'it-may be attached tothe ignitor and simply brought into contact with'the heater. This ignitor is especially adaptable tocatalytic heaters as described in co-pending application entitled METHOD AND APPARATUS FOR CATALYTIC IG- NITION OF EARTH FORMATIONS, Ser. No. 889,059, now abandoned, filed of even date herewith. It would be necessary to raise the temperature to a level at which natural gas would react with air in the presence of a catalytic material, i.e.; approximately 250 F. A guide means would be needed in the heater for receiving the ignitor.

FIG. 3C illustrates a catalytic heater 38 which is of the same basic design as the catalytic ignitor described in FIGS. 4 and 4A as well as the catalytic heater described in Ser. Number 92,836. The catalytic heater has contact electrodes 52 and heating element 44 contained therein which has been schematically illustrated in FIG. 3B. The catalytic heater 38 has a catalytic material 37 on its outer surface and a glass fiber portion 39 surrounding a distribution pipe 66 having perforations 34 therein. The heating element 44 is embedded in the glass fiber material 39 and terminates in contact electrodes 52 at the upper end of the catalytic heater 38. Once the catalytic heater 38 has been located in a FIGS. 4 and 4A a fuel gas preferably containing methane is flowed down wellpipe to the heater 38 and passes through perforations 34, eventually coming into contact with catalytic material 37. Air is flowed down the annulus to come into contact with the exterior surface of the heater 38. The fuel gas and air mixture will not catalytically react at normal bottom hole tempera tures, therefore, it is necessary to raise the temperature of the fuel mixture to its reaction temperature of approximately 250 F. As in the catalytic ignitor described in FIGS. 4 and 4A the termination of reaction conditions may be monitored by use of a thermocouple.

FIGS. 4 and 4A illustrate a catalytic ignitor for use in igniting fuel fed heaters. The catalytic ignitor is of the same design and operates in the same manner as the catalytic heater disclosed in Ser. No. 92,836. This ignitor is also especially adaptable to igniting the heaters described in co-pending application entitled METHOD AND APPARATUS FOR IGNITION AND HEATING OF EARTH FORMATIONS, Ser. No. 889,061 filed of even date herewith.

FIG. 4 shows an ignitor 38 located in a wellbore inside of casing 12 and extending into tubing 14. The ignitor is seated in seating nipple 22 by contacting a nogo flange 46. The catalytic surface 37 is sealed from the interior of the tubing 14 by O-rings 48, and is separated from the seating nipple 22 by lower stand-off member 62. Air is flowed down the annulus between the casing 12 and tubing 14 to be in communication with the exterior of the ignitor 38 and to force fluids from the wellbore away from the formation adjacent the wellbore. A hydrogen containing fuel gas is flowed down the tubing 14 and enters gas inlet ports 68 located in upper stand-off member 32. Fuel gas then flows down pipe interior 66 to the interior of the ignitor 38. Upon the hydrogen contacting the catalytic surface 37. the hydrogen will react with the air.

The state of the reaction can be monitored by utilization of thermocouple 64, which is attached to an armored thermocouple cable 40, which extends to the surface where an indicator (not shown) reflects the temperature at the ignitor corresponding to the electromotive force generated by the thermocouple 64. The thermocouple cable 40 is connected to the ignitor by cable head and thermocouple hanger assemblies 24. The reaction temperature of the hydrogen and air at the catalytic surface 37 is sufficient to initiate a catalytic reaction of natural gas and air, whereupon the hydrogen portion of the fuel may be terminated. Whether there is a sufficient temperature for natural gas and air to react in the presence of the catalyst is determined by information received from thermocouple 64. Once a natural gas and air reaction has commenced, the temperature will be sufficient to cause a natural gas and air mixture to burn at the heater.

The make-up of the catalytic portion of the ignitor is depicted by a cross-section of the ignitor shown in FIG. 4A. There is shown a screen type retaining means 36 adjacent the catalytic surface 37. Baffling material 39, preferably a fiberized silica material such as FIBERGLASS or CERAFELT is positioned between the retaining means 36 and the wall of the pipe interior 66. In the catalytic section, the pipe interior 66 is perforated to provide a passageway for the fuel gas to reach the catalytic surface 37. The function of the baffling material 39 is to difluse the fuel gas so that it spreads over the entire catalytic surface 37. This baffling material 39 is arranged such that there is only a slight pressure drop as the fuel gas exits the ignitor 38. The screen type retaining means 36 is rigid enough to provide shape to the catalytic area of the heater so that it is not easily deformed.

The catalytic material used in the ignitor may be selected from a wide list of materials and forms no part of this invention. The preferable catalyst is platinum on a heat resistant support such asasbestos or ceramic material. Other catalysts suitable for oxidation of the fuel gas include the platinum group metals and their oxides. Many other catalytic materials may be used in this reaction and are well known to those of skill in the catalytic material art.

Modifications may be necessary in the upper portion of the ignitor 38 to adapt it to conform to the requirements of specific heaters. Care should be taken regarding the fuel and air mixture present in the wellbore. If the mixture contains approximately '5 to 15 percent methane, with the remainder air, it is explosive. Also, if the mixture is approximately 4 to 74 percent hydrogen with the remainder air, explosions occur. Therefore, in the operation of this ignitor to avoid explosive mixtures, an air to fuel ratio of at least 25 to one should be used.

Utilization of a hydrogen-natural gas fuel mixture allows for a higher fuel injection rate. If hydrogen alone were used, approximately 6 cu. ft. of hydrogen per hour per square foot of catalyst surface could be injected. With a natural gas-hydrogen mixture, injection rates can be increased to 20 to 25 standard cu. feet per hour per square foot of catalyst surface. Since hydrogen is not readily available in large quantities, it is best to operate the ignitor with the hydrogen-natural gas fuel mixture only until the natural gas starts to react. At that point the hydrogen is no longer necessary. The fuel injection rate of natural gas alone is ordinarily 20 to 45 standard cu. ft. per hour per square foot of catalyst surface. This natural gas-air reaction will go to flame given a high enough fuel injection rate. Once flame is initiated, the heater is ignited and the ignitor 38 can be withdrawn from the wellbore by cable 40. In this regard, ignitor 38 is smaller in diameter than tubing 14 to permit withdrawal through the tubing 14.

Referring to the ignitor illustrated in FIG. 4, it is presumed that a heater would be surrounding the catalytic portion of the ignitor and the heater would be encircled by a heatshield to protect the casing 12. Perforations 30 are shown below the ignitor 38 and allow heated air to enter the formation.

While particular embodiments of the present invention have been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

l. The combination of apparatus for providing heat in a wellbore having well pipe therein, comprising: an ignitor including a housing, energy source means located in said housing and electrical connection means on said energy source means; and a catalytic heater located adjacent the ignitor having a fluids flow channel therethrough, said heater. configured so that the flow channel in said heater is arranged to communicate with the interior of the well pipe, said heater including electrically energized heat producing means.

2. The apparatus of claim 1 wherein said catalytic heater has electrical contacts for mating with the electrical connection means of said ignitor, and where the energy source means comprises at least one battery.

3. The apparatus of claim 1 wherein said catalytic heater comprises a tubular member having a catalytic material at the end of the well pipe; flowing one component of a fuel mixture through the wellpipe and through the catalytic material; flowing the remaining component of the fuel mixture down the annulus and into contact with the exterior surface of the catalytic material, and initiating a catalytic reaction of the fuel mixture by providing a source of electrical energy in the wellbore in the vicinity of the catalytic heater and transmitting the electrical energy in the form of heat to the catalytic heater. 7

6. The process of claim 5 wherein the fuel mixture component flowing through the catalytic material comprises a fuel gas and the remaining fuel mixture component flowing down the annulus comprises air.

7. The process of claim 5 wherein the source of electrical energy comprises at least one battery and trans-.

mittal of the electrical energy in the form of heat to the catalytic heater '5 accomplished by providing the catalytic material with a resistance heating element and connecting the battery with the heating element.

# i i i l 

2. The apparatus of claim 1 wherein said catalytic heater has electrical contacts for mating with the electrical connection means of said ignitor, and where the energy source means comprises at least one battery.
 3. The apparatus of claim 1 wherein said catalytic heater comprises a tubular member having a catalytic material on its exterior surface and perforated conduit means extending the length of the interior of the tubular member adjacent the catalytic material.
 4. The apparatus of claim 1 wherein the electrically energizable heat producing means in said catalytic heater comprises a resistive element which heats when electrical energy flows therethrough.
 5. A process of providing heat in a wellbore having well pipe therein and an annular space between the well pipe and wellbore, comprising: locating a catalytic material at the end of the well pipe; flowing one component of a fuel mixture through the wellpipe and through the catalytic material; flowing the remaining component of the fuel mixture down the annulus and into contact with the exterior surface of the catalytic material, and initiating a catalytic reaction of the fuel mixture by providing a source of electrical energy in the wellbore in the vicinity of the catalytic heater and transmitting the electrical energy in the form of heat to the catalytic heater.
 6. The process of claim 5 wHerein the fuel mixture component flowing through the catalytic material comprises a fuel gas and the remaining fuel mixture component flowing down the annulus comprises air.
 7. The process of claim 5 wherein the source of electrical energy comprises at least one battery and transmittal of the electrical energy in the form of heat to the catalytic heater is accomplished by providing the catalytic material with a resistance heating element and connecting the battery with the heating element. 